The present invention relates to fuel injection systems and pertains more particularly to a conventional fuel injection nozzle assembly with a retraction type valve added within the assembly.
Compression ignition engines commonly employ fuel injection nozzles for delivering a timed injection and metered quantity of fuel into the engine combustion chamber. Such nozzles are normally controlled by a pressure-responsive check valve to prevent dribbling of fuel into the combustion chamber between injection strokes. Most injection systems also employ a retraction type delivery valve at the fuel pump outlet for establishing a sharp decrease in fuel pressure in the fuel line to the fuel injection nozzle at the end of an injection cycle.
The injection pump and thus the retraction valve are normally located some distance from the injection nozzle itself, resulting in the entrapment of a relatively large volume of fuel in the fuel line between the injection and retraction valves. For this reason and because fuel is compressible, it has been found that an abrupt termination of the injection of fuel into the engine, at the end of the injection cycle does not occur. This is true despite the numerous improvements made in injector nozzles.
The following patents are examples of the prior art construction of injection nozzles. U.S. Pat. No. 3,382,851 issued May 14, 1968, to De Luca; U.S. Pat. No. 3,511,443 issued May 12, 1976, to Glikin, et al.; U.S. Pat. No. 3,620,456 issued Nov. 16, 1971, to Berg, et al.; U.S. Pat. No. 3,630,454 issued Dec. 28, 1971, to Mowbray; and U.S. Pat. No. 3,788,546 issued Jan. 29, 1974, to Bailey, et al.
As pointed out above, because of the conventional arrangement of injection pump cutoff or retraction valves and injector nozzle assemblies, an abrupt termination of the injection of fuel into the cylinder at the end of an injection cycle does not occur. The slow termination of the injection cycle, during which fuel is injected at relatively low pressure increases the amount of unburned hydrocarbons and smoke emitted into the atmosphere by an engine. This also results in a waste of fuel since the after-burned fuel contributes inefficiently, if at all, to the power output of the engine.